In configurations with ungrounded reference potential (jumper between M and functional ground removed, see the figure in the "Configuration of an ET 200M with ungrounded reference potential" chapter), in the case of a polarity reversal an internal electronic fuse is triggered and this regenerates after approx. 30 seconds.

With a configuration with grounded reference potential (bridge inserted between M and functional earth) when connection this brings about a short circuit current via this bridge and the functional earths.
In doing so, the IM153‑2 is not damaged if a protection is built in before the module which is designed in accordance with the cross-section of the connection line.